FIG. 10 shows a general conventional vapor-compression type refrigerator. The vapor-compression type refrigerator shown in FIG. 10 comprises a compressor 101, a radiator 102, an expansion valve 103 and an evaporator 104. These members are connected to one another through pipes, and refrigerant is circulated as shown with hollow arrows in the drawing.
The operation principle of the vapor-compression type refrigerator is as follows. The pressure and temperature of the refrigerant are increased by the compressor 101, the refrigerant enters radiator 102 and is cooled. Then, the high pressure refrigerant is compressed under the vapor pressure by the expansion valve 103, heat of the refrigerant is absorbed by the evaporator 104 and the refrigerant is vaporized. The refrigerant coming out from the evaporator 104 returns to the compressor 101. In this apparatus, carbon dioxide which does not destroy the ozone layer and has extremely small global warming coefficient is used as the refrigerant.
However, as compared with a refrigerator using commonly used flon as the refrigerant, the vapor-compression type refrigerator using carbon dioxide as the refrigerant has lower coefficient of performance (COP) which is energy efficiency. When both the refrigerators have the same refrigeration abilities, the vapor-compression type refrigerator needs more electricity than the refrigerator using flon as the refrigerant. Thus, more fossil fuel is required as energy, and even if the global warming coefficient of the refrigerant itself is small, more carbon dioxide is discharged as a result. Therefore, it is necessary to enhance the COP of the vapor-compression type refrigerator using carbon dioxide as the refrigerant, and various configurations and methods have been proposed.
The following apparatus for enhancing the COP have been proposed (patent documents 1 to 3). In a refrigerator shown in FIG. 11, a compressor 201 is driven by a prime mover 205, a refrigerant compressed by the compressor 201 is cooled by a radiator 202 and then, the refrigerant passes through an expander 204 on which an expansion ratio controller 203 is mounted. The expander 204 assists the compressor 201 in driving through a main shaft 213. The refrigerant expands in the expander 204, heat of the refrigerant is absorbed from outside in the evaporator and vaporized and then, the refrigerant returns to the compressor 201. The compressor 201, the radiator 202, the expander 204 and the evaporator 206 are connected to each other through a pipe 207 and constitute a circuit. To enhance the performance and reliability, an oil separator 208 and an accumulator 209 are provided in some cases.
The expansion ratio controller 203 is controlled by calculation means 210. A temperature sensor 211 and a pressure sensor 212 are mounted for detecting a state of a refrigerant on the side of an outlet as input to the calculation means 210.
In the refrigerator having such a configuration, since the driving operation of the compressor 201 is assisted by an expanding force of the refrigerant by using the expander 204, the total amount of energy to be used is reduced, and the COP can be enhanced.
That is, when the conventional expansion valve is used as the expanding means like a pressure—enthalpy state diagram, i.e., a so-called Mollier diagram which shows a state of a refrigerant in a refrigeration cycle using carbon dioxide as the refrigerant, the refrigerant is equally enthalpy expanded, but it is equally entropy expanded (shown with dotted lines) by the expander, and power recovered by the expander is utilized, thus, the total efficiency can be enhanced.
In a refrigerator shown in FIG. 13, a compressor 401 is driven by a prime mover 405, a refrigerant compressed by the compressor 401 is cooled by a radiator 402 and then, when the refrigerant passes through an expander 403, a power generator 404 connected to the expander 403 generates electricity (patent documents 1 and 2). Then, the refrigerant expands in the expander 403, heat of the refrigerant is absorbed from outside in an evaporator 406 and the refrigerant is vaporized and then, the refrigerant again returns to the compressor 401.
According to this apparatus, the expansion force of the refrigerant rotates the power generator 404 to generate electricity. Since this electricity is utilized, the total energy to be used can be reduced, thereby enhancing the COP.
As such a power generator 404, an exciting apparatus is used (patent document 4). FIGS. 14 and 15 show a refrigerator disclosed in patent document 4. As shown in FIG. 14, according to this refrigerator, refrigerant is circulated through a compressor 501, a condenser 502, a liquid receiver 503, an expander 504, and an evaporator 505 in this order. The expander 504 is provided with a power generator 506 coaxially connected to its drive shaft. The refrigerator comprises a superheat detector 512 provided in an outlet of the evaporator 505 for detecting a superheat of the refrigerant, a controller 511 for controlling exciting current of the power generator 506 based on a signal of the superheat detector 512, a rectifier 508 for converting AC generated by the power generator 506 into DC, and a capacitor 510 for recovering DC electricity.
In the case of this refrigerator, the exciting current (i.e., current amount flowing through an exciting coil) of the power generator 506 is adjusted to control the power generator 506, a torque of a load of the power generator 506 is increased or reduced to control the rotation of the expander 504, thereby adjusting the flow rate of the refrigerant, and recovering the electricity generated by the power generator 506 efficiently into a capacitor 510.
The power generator 506 inputs a driving force by a drive shaft foxed to the other end of a rotor to generate electricity. The power generator 506 is provided with a brush. The brush slides on a slip ring and supplies exciting current to a rotor coil. If the expansion rotation of the refrigerant rotates the drive shaft, a magnetic field is produced by exciting current supplied to a rotor coil, an electromotive force is generated in a stator coil, and the electromotive force is output by the stator coil as AC power.
An exciting unit 507 for producing the exciting current of the power generator 506 has a circuit configuration shown in FIG. 15. The exciting unit 507 supplies, to the power generator 506, an exciting current control signal which is output from a controller 511 as an input signal, and exciting current from the exciting unit 507 as an output signal.
That is, an exciting current control signal which is output from a controller 511 is applied to a base of a npn-type transistor Tr604 (Tr604, hereinafter). An emitter of the Tr604 is connected to a minus terminal of the power generator 506, and a collector of the Tr604 is connected to a rotor coil 602 of the power generator 506 through a resistor 605. A base of a transistor Tr603 (Tr603, hereinafter) is connected to a collector of the Tr604, an emitter of the Tr603 is connected to a minus terminal of the power generator 506, and a collector of the Tr603 is connected to a plus terminal of the power generator 506. With this, if the exciting current control signal applied to the base of the Tr604 from the controller 511 is increased, the Tr604 is brought into conduction and the exciting current flowing through the rotor coil 602 is increased, and if the exciting current control signal applied to the base of the Tr604 is reduced, the exciting current is reduced.
The controller 511 which outputs the exciting current control signal controls the exciting current control signal which is output to the exciting unit 507 such that the flow rate of the refrigerant becomes the appropriate value based on temperature information of the refrigeration cycle. For example, when a circulation amount of refrigerant is small, the exciting current of the power generator 506 is reduced, the load torque is reduced, and the number of revolutions of the expander 504 is increased. When the circulation amount is large on the other hand, the exciting current of the power generator 506 is increased, the load torque is increased, and the number of revolutions of the power generator 506 is reduced. Further, AC generated by the power generator 506 is converted into DC through the rectifier 508, a charging voltage is controlled substantially constant through a variable load resistor 509, and charges the capacitor 510 is charged with electricity.
The exciting current is controlled by the power generator 506 having the rotor coil 602 and the exciting unit 507 which supplies the exciting current to the rotor coil 602, thereby controlling the number of revolutions of the expander 504.
A patent document 5 describes a wind power generator in which an output of a permanent magnet type synchronization power generator connected to a windmill through a shaft is converted by using an AC-DC converter (variable-speed inverter), and a variable-speed inverter is controlled, thereby controlling the output voltage of the power generator and variable-speed of the number of revolutions of the power generator.
Further, a patent document 6 describes a magnetic pole position is estimated by a position estimating device from output current and terminal voltage of a permanent magnet type synchronization power generator, and then, a torque of the power generator is controlled.
[Patent Document 1] Japanese Patent Application Laid-open No. 2000-241033
[Patent Document 2] Japanese Patent Application Laid-open No. 2000-249411
[Patent Document 3] Japanese Patent Application Laid-open No. 2001-165513
[Patent Document 4] Japanese Patent Application Laid-open No. H1-168518
[Patent Document 5] Japanese Patent Application Laid-open No. 2000-345952
[Patent Document 6] Japanese Patent Application Laid-open No. 2002-354896
However, in the case of the configuration described in the patent document 4, since a rotor of the power generator includes an exciting unit and a coil, its weight is increased, and its configuration is complicated. Further, since current flows through the exciting unit, there is electricity loss in the rotor, and the power generation efficiency is low.
Further, since the number of revolutions of the power generator is controlled by adjusting the exciting current, in the case which the number of revolutions exceeds the adjusting range of a narrow exciting current, the expander can not be controlled. Thus, it is difficult to optimize the refrigeration cycle, and the efficiency of the refrigeration cycle can not be optimized.
In the case of the control of the power generator described in a cited document 5, since the rotor does not have an exciting element and a coil, the weight on the side of the rotor is reduced, current loss in the rotor is reduced and thus, the power generating efficiency is enhanced, but there is no description concerning a method for detecting a position of the magnetic pole of the power generator. When a permanent magnet type synchronization power generator having no exciting unit is used, in order to control the power generator, it is necessary to detect the position of the magnetic pole of the power generator. To detect the magnetic pole position of the power generator, it is conventionally necessary to use a rotation position sensor such as an encoder. Thus, when the encoder and the power generator are integrally formed, it is necessary to bring a rotation shaft out from a shell for the encoder. To this end, a countermeasure such as a shaft seal against the pressure is required, and the reliability is deteriorated.
In a wind power generator and the like, in order to constantly maintain DC irrespective of the rotation speed of the permanent magnet type synchronization power generator, patent document 6 discloses a technique in which a magnetic pole position is estimated using current without using an encoder, thereby controlling the power generator. In a heat pump apparatus, however, in addition to merely maximize the output of the power generator, it is required to control to optimize the efficiency of the refrigeration cycle while efficiently utilizing the output of the power generator.
Further, at the time of actuation, the expander can not forcibly be rotated, and the reliability of the refrigeration cycle is deteriorated.
Therefore, the present invention has been accomplished to solve these problems, and it is an object of the invention to provide a heat pump apparatus in which the weight on the side of a rotor is reduced, the rotor does not have an exciting unit and a coil and thus, since electricity does not flow through the exciting unit and coil, there is no electricity loss in the rotor, the power generating efficiency is enhanced, the configuration on the side of the rotor is simple, the cost thereof is reduced, and the usefulness of the power generator can be utilized.
It is another object to provide an efficient and reliable heat pump apparatus. That is, an expander can be controlled with a wide number of revolutions, the efficiency is optimized, a permanent magnet type synchronization power generator can be controlled without the rotation position sensor, the reliability is enhanced in terms of sealing ability, the expander can be rotated forcibly at the time of actuation thereof, the actuation performance is enhanced, and the reliability of the refrigeration cycle is enhanced.